Subwavelength optical localization with toroidal excitations in plasmonic and Mie metamaterials

Abstract

Since the performance of electronic circuits is becoming rather limited in face of intensively increasing of amount of information and related operations, all‐optical processing offers a promising strategy for future information system. It would benefit a great deal if the all‐optical processing could be implemented within the developed electronic chips of nanoscale structures. In that it is highly desirable to break the diffraction limit of light for achieving effective light manipulations with deep subwavelength structures compatible with the state‐of‐the‐art nanofabrication processes. It is of fundamental importance to get subwavelength optical localization, that is, squeeze light wave into subwavelength space for achieving freely manipulating of light fields. This review summarizes the development in realizing subwavelength optical localization by exciting toroidal mode in photonic metamaterials. The toroidal excitations in plasmonic metamaterials and Mie resonant metamaterials, in 3D structures and planar metamaterials, with single or few layers in spectral regime from microwave to optical frequencies are surveyed. Based on the discussion on the configurations of toroidal excitations, the recent development on toroidal‐related optical scattering control actively manipulates the toroidal excitations, and promising applications are further investigated and highlighted.

Diatomic terahertz metasurfaces for arbitrary-to-circular polarization conversion

“…Calculations show that electric dipole (ED), magnetic dipole (MD), toroidal dipole (TD), electric quadrupole (EQ) and magnetic quadrupole (MQ) are the main contributing resonances for the scattering properties. 29–33 The detailed simulation process is as mentioned in ESI Note 7 †. The modes that dominate the multipole decomposition of scattered power on the two circularly polarized channels are different due to the overlap of multiple resonant modes.…”

Polarization‐Multiplexed Silicon Metasurfaces for Multi‐Channel Visible Light Modulation

“…Moreover, the planar characteristics of metasurfaces make them easier to design, integrate multiple functions, and fabricate. Recently, plenty of functional metasurface devices have been reported, including metagratings, [ 5–8 ] high quality factor devices, [ 9,10 ] spontaneous emission control, [ 11–13 ] magnetic mirrors, [ 14 ] cloaking, [ 15–20 ] optical vortex beam generators, [ 21–25 ] and so on. [ 26–39 ]…”

Active Control of Terahertz Toroidal Excitations in a Hybrid Metasurface with an Electrically Biased Silicon Layer

“…[ 15–21 ] Different from electric and magnetic excitations in traditional multipole expansions, toroidal excitations arise from the decomposition of the momentum tensors with currents flowing on the surface of the torus along its meridians. [ 22–25 ] The toroidal excitations taking advantage of weak free‐space coupling properties are beneficial for achieving ultra‐high‐ Q response in a metamaterial, which has inspired numerous applications, [ 24 ] such as metaswitches, [ 26,27 ] photodetectors, [ 28 ] metamodulators, [ 29 ] metasensors, [ 30–32 ] and nonlinear harmonic signal generators. [ 33 ] Their unique field localization configuration is also helpful for avoiding the huge Ohmic dissipation on a metal surface and thus low‐power nonlinear processing.…”